Electromagnetic switch contactors are usually dimensioned electrically and magnetically so that little electric power is to be applied in the holding state of the magnet armature (e.g., German Patent Application 195 26 038 A1). This is recommended because devices of this type are in the holding state most of their operating time. Power consumption in the holding state has the disadvantage that the device heats up. Power losses of a few watts are typically expected in the holding state. For vacuum switchgears, considerably higher power losses may occur. Considering the fact that contactors or switches are mostly combined in one switch box, active measures for dissipating heat must be taken.
The use of electronics has not yet resulted in satisfactory improvement. Thus, known electronic approaches for electromagnet systems include controlling the power requirement via pulse width modulation. This method results in the need for generating increasingly narrower pulses in the circuit as power consumption decreases. As the pulses become narrower, harmonic components appear, which cause problems in electromagnetic shielding and compatibility.
A magnet system having a circuit system for generating pulse trains to regulate power consumption is presented in German Patent Application 39 10 810 A1 or in German Patent Application 195 26 038 A1, for example.